Diagnostic Aids

Check for poor connection, rubbed-through wire insulation or a broken wire inside insulation at PCM and IAC motor. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection, and damaged harness. Ensure air intake system is not restricted. Check throttle body for blockage and carbon build up. Clean as necessary. Inspect for a large vacuum leak at brake booster or PCV. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC DIAGNOSTIC PROCEDURES article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
2. Using scan tool, read DTCs. If any other DTCs are set, diagnose them first before proceeding. If no other DTCs are set, go to next step.
3. Start engine. Turn all accessories off. Using scan tool, monitor ENGINE SPEED and command engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. If ENGINE SPEED remains within 50 RPM of desired RPM for each command, check for an intermittent problem. See DIAGNOSTIC AIDS . If operation is not as specified, go to next step.
4. Disconnect IAC harness connector. Install IAC Noid-Light (J37027A) in IAC harness connector. With engine running, monitor noid-lights while commanding engine speed up to 1500 RPM, down to 500 RPM, then back up to 1500 RPM. Both noid-lights should cycle Green and Red, but not OFF as RPM changes from 500 to 1500 RPM. If noid-lights flash as specified, go to step  6. If noid-lights do not flash as specified, go to next step.
5. Check IAC "A" high (Blue wire) and low (Blue/White wire) and "B" high (Blue/Red wire) and low (Blue/Black wire) circuits for an open, short to voltage, short to ground or poor connection at PCM. If a problem is found, repair as necessary. Retest system. If no problem is found, go to step  9.
6. Ensure throttle stop screw has not been tampered with. Check for stuck IAC valve or throttle linkage. Check for restrictions, collapse or blockage in air intake system. Check throttle body bore and IAC valve for excessive deposits. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
7. Check for faulty connection at IAC valve harness connector. If faulty connection is found, repair as necessary. Retest system. If connection is okay, go to next step.
8. Replace IAC valve. Retest system.
9. Replace PCM. Retest system.